Hero: Beth

Beth is a Scout hero, with the following Leader trait:

Whenever Beth defeats her main target* or uses a charge attack, the area around the target emits a buff. Overlapping buff areas merge into one bigger area (max 7 space radius on one area, otherwise new ones will be created). When this happens, the duration refreshes as well.
Any survivor standing in this area deals a % of their target's current HP as extra damage. Essentially, the more HP the enemy has, the higher the damage buff.

As an example, if the buff grants survivors a 10% of the target's current HP as extra damage, and the target has 100/100 HP - the first attack will deal 10 extra damage. If the enemy is down to 70/100 HP, then the extra damage will be 7.

Beth does not need to be the leader for other survivors to benefit from the area buffs. However, if Beth is the leader, then all survivors' kills and charge attacks will emit the buff or merge to create a bigger area.

*When attacking using weapons that can target more than one enemy, the one that you hover on is the main target.